The aforementioned proteins receive signals from a subset of tumor necrosis factor receptors (TNFRs) that contain a death domain. A second class of TNFRs interact with the TRAF molecules to transmit a signal that leads to cell proliferation instead of cell death. Mass spectrometry and Western blot analysis have been applied to TRAF2 to define the minimal interacting domain, to define the interaction surface of CD30 and CD40 in preparation for a full structural analysis of a TRAF/receptor domain complex.